(1) Field of the Invention
The present invention relates to a cutting plotter for producing a predetermined shape from a sheet-shaped cutting medium such as a paper, a marking film, and so on, which are used, for example, for an outdoor signboard or a decoration of a windshield glass or a show window, and more particularly, to an angular initialization method for orientating a cutting edge portion in a cutting plotter wherein a direction of an edge portion of a cutter main body can be located to point in a predetermined direction shortly before a cutting operation is commenced.
(2) Description of the Related Art
In such a kind of cutting plotter as described above, it is generally known that a host computer feeds various cutting data, including information required for a cutting operation, and a cutter member is shifted in an X direction or a Y direction in an X-Y coordinates which are defined in a mutual relationship with a cutting medium, and as a result, the cutting medium is cut out in a predetermined shape. In the beginning of the cutting operation, the cutter member is located at a position which corresponds to a starting point of a preselected shape to be cut in the cutting operation, based on the cutting data fed from the host computer. Then the cutter member is lowered in order to commence the cutting operation, and the cutting operation is performed in such a manner that the cutting member moves along the shape preselected by the host computer. Then, at the end of the cutting operation, the cutter member is raised upward so as to depart from the ending point of the shape to be cut out, and thus, one cycle of the cutting operation is completed. Normally, such a cutting operation is repeated in the same cutting medium, therefore, a plurality of shapes, such as letters or figures are obtained from the single cutting medium.
The cutter member has a column-shaped cutter supported so as to be able to rotate freely, and there is provided a cutting edge portion at the lower end of the outer surface of the cutter. The cutting edge portion is formed to have an inclined cutting edge surface, and there is provided a pointed end at the front end of the cutting edge portion. The pointed end of the cutting edge portion is formed to be offset from a rotational axis of the cutter. This is for causing a rotational moment which is transferred from the cutting medium to the cutter through the pointed end of the cutting edge portion, and such a rotational moment is caused based on the offset arrangement of the pointed end from the cutting edge portion. Therefore, the cutting edge portion of the cutter is designed to be always likely to point in the cutting direction. Such a construction is known to the public, as shown in the Japanese Utility Model 49-19322.
However, due to the nature of the cutter which is freely rotatable as described in the foregoing description, is not always desirable to accurately control the direction of the cutting edge portion so as to coincide with the predetermined cutting direction.
For this reason, generally, at the end of the cutting operation this has been utilized to detect an angular dislocation of the cutting edge portion, with respect to the rotational axis of the cutter main body. These detected angular dislocations are memorized into a RAM (Random Access Memory) so as to renew the previous data by the latest data upon receiving each detected data. This is because the cutting edge portion is placed to point accurately to the cutting direction; i.e. the direction of a last part of line segment of the predetermined shape to be cut out, at the end of the cutting operation. The memorized angular dislocation data is utilized to calculate the direction of the cutting edge portion and to control the cutting edge portion in the next cutting operation.
However, when the cutting plotter itself is turned on or when the cutting plotter is in a brand-new condition, an operation is thus carried out for the first time, it should be noted that there is no information available at that time, since no data is memorized as cutting data of the previous cutting operation. Accordingly, it was necessary to perform an angular initialization for orientating the direction of the cutting edge portion of the cutter to point the predetermined direction by using any effective method.
Various methods are proposed, conventionally, such as angular initialization methods for the cutting edge portion. The one shown in FIG. 5 is the method which does not require any particular device to be newly added.
The angular initialization in the method shown in FIG. 5 is carried out in such a manner that, in the case that a cutting medium 1 is cut out by a cutter 30, that when a cutting operation is started from a starting point A toward a corner point B, an actual cutting operation is commenced from the other point A' which is located to be spaced out from the point A in the opposite direction of point B. The initial cutting operation is carried out in such a manner that the cutter 30 shifts from the point A' to the point A along a straight line which is indicated as a broken line in the drawing. Since the pointed end of the cutting edge portion of the cutter 30 is supported to be freely rotatable around the rotational axis, and is offset from the rotational axis, a locus of the pointed end of the cutting edge portion is depicted as is shown by a solid line in the drawing. That is, the direction of the cutting edge portion is gradually changed to coincide the same direction as a line segment AB. Thus, the direction of the cutting edge portion is located to point in a predetermined direction shortly before the cutter 30 reaches the point A.
In such a conventional method, it might be no problem if an angular dislocation of a cutter 30 with respect to the line segment AB is small. However, in the case that the angular dislocation becomes large so as to approach to approximately 180 degree, that is, if the direction of the cutting edge portion is located to point in the exactly opposite direction against the cutting direction at the beginning of the cutting operation, the rotational moment, which should be caused around the rotational axis of the cutter 30 due to the offset arrangement of the pointed end, is suppressed because a resistance force loaded from the cutting medium to the cutter 30 becomes large enough to cancel this rotational moment.